Syrian rebel fighters have freed at least 50 people held captive by an al-Qaida-linked faction after clashes between rival sides deepened within the country's opposition-held areas in the north, activists said.

The rebel infighting in Raqqa – a bastion of the al-Qaida-linked group known as the Islamic State of Iraq and the Levant (Isil) – reflects a widening war within a war in Syria, this one against radical extremists...